The present invention concerns a control method and apparatus for an aircraft when taxiing. More particularly, but not exclusively, this invention concerns a method of controlling the motion of an aircraft during taxiing on the ground. The invention also concerns a control system for use in performing such a method, and associated software. The invention also concerns an aircraft employing such a control system.
When controlling the motion of an aircraft during taxiing on the ground, turning of the aircraft may be controlled by means of a steerable landing gear. The present invention principally concerns control of the turning of the aircraft when a steerable landing gear (for example the principal steerable landing gear) is operating in a “free-to-caster” mode. Control systems have been proposed in the prior art concerning how to control the steering/turning of the aircraft in various ways.
WO 2014/076486 concerns a landing gear force and moment distributor system for a left and right main landing gear (MLG) of an aircraft. Each MLG comprises a bogie having an actuator arranged to brake and/or drive one or more wheels. The force and moment distributor system comprises a distribution module arranged to receive an input demand including (a) a longitudinal force input demand corresponding to a desired braking or driving force along the longitudinal axis for the landing gear and (b) a moment input demand corresponding to a desired moment about the vertical axis for the landing gear (e.g. a steering/turning amount). The received input demand is used to calculate an output command comprising, for each bogie, (a) a longitudinal force output command corresponding to a braking or driving force along the longitudinal axis to be applied to the bogie to achieve the longitudinal force input demand, and (b) a moment output command corresponding to a braking or driving force along the longitudinal axis to be applied to the bogie to achieve the moment input demand.
U.S. Pat. No. 8,521,365 relates to a method for providing lateral control of a taxiing aircraft with left and right main landing gear assemblies and a steerable nose landing gear (NLG), when the NLG is in a “free-to-caster” mode. In such a mode, the NLG aligns with the direction of travel of the aircraft but cannot be used to control steering of the aircraft; other means must be used. In U.S. Pat. No. 8,521,365, command orders are received relating to a desired amount of steering of the NLG wheel using the same apparatus as would be used when the NLG is in a steerable mode (in which mode, such command orders are used to directly steer the NLG with actuators provided for such a purpose). Such command orders are converted so as to control the MLG brakes/engines to cause the lateral movement of the caster aircraft corresponding to the same lateral movement that would be caused had the command orders been used to effect direct steering of the NLG.
The present invention seeks to provide an improved a method of controlling the motion of an aircraft during taxiing on the ground, when the steerable landing gear is operating in a “free-to-caster” mode.